Speed regulator



Jung 17, 1930.

M. STOLLER ET AL SPEED REGULATOR iled June 23. 1927 by l' Arron/vir June 11, 1930. H.-M. STOLLER er M 1,763,909

SPEBD REGULATOR FiledvJune 23. 1927 3 Sheets-Sheet 2 By l 'www/wn .Immv 17, 1930.

`H. M. sToLVLER El' l- SPEED RoULA'x-on Filed June 25. 1927 3 Sheets-Sheet A3 y ffl/@HM 57mm? Mmm-'v' [0M/N0 Mmmm W K Arm/awa,

Patented June 17, l1930 y y UNITED STATES PATENT, OFFICE HUGHr M. STOLLER, F MOUNTAIN'LAKES, NEW TERSEIY, AND EDMUNIIE. HOB/TON, 0F BROOKLYN, NEW YORK, ASSIGNORS T0 BELL TELEPHONE LABORATORIES, IN-

CORPORATED, 0F NEW`YORK, N. Y., A CORPORATION OF NEW YORK SPEED REGULATOR Application illed .Tune 23, 1927. Serial No'. 200,799.

This invention relates to speed regulating systems and particularly to systems for synchronously operating the moving scanning mechanisms at the transmitter and at the receiver, respectively, of television systems, and for framing the image at the receiver. It is a continuation in part of ap-u plication, Serial No. 181,314, filed April 6, 1927.

Close synchronization of the moving scanning elements at the transmitter and receiver of a television system is required. Such moving elements may be driven by direct current motors in which case means must be provided for maintaining these motors in synchronous operation.

In accordance with this invention a high frequency alternating current generator is mechanically coupled to the motor at the controlling station `and the current therefrom is suppl ed to a similar machine coupled to thel direct current motor at the controlled station and is thereby voperated as a synchronous motor. The stator Aof the high frequenc machine at the receiving station is'provi ed with a worm gear 'rotated by a hand o erated worm for permitting framing o lthe received ima e. This arrangement is operable but it as vtwo disadvantages. First, it is diilicult to synchronize the machines las it is diicult to close the armature circuit of thehigh frequency motor at the right phase position with the mo- I tors-running at very closelythel same speed, and, second, the stator 'of the -highfrequency machine at the receiving stationmay have to' be turned t-hrough a large angle` when` framing the image, which is dificult to accomplish as the movement can not be made rapidly without throwing the motor out of step. In accordance with a further aspect of the invention, these disadvantages are over# come bykthe 4provisyion'of a, low frequency interlock in addition to thehi h interlock above described. Tix

,e 'low frequency interlock provides an approximate synchronization within a single A `limited range of phase positions thereby greatly facilitating the processes of synchronizing on the high frequency and of framing.

frequencyv i control'device, the space current of which is 'site commutator The invention is illustrated in the accompanying drawings in which Figs. 1, 2 and 3, placed end to end, show a television system employing the circuit arrangement of the present invention for synchronously operating the driving motors, and Fig. 4 shows the arrangement for mounting the motors at the receiving stat-ion.

This invention as illustrated in the drawing comprises a television system 'in which the scanning discs at the transmittingl and receiving stations are driven by two-pole direct current motors individual thereto. The speed of the motor at one station, which will hereinafter be designated as the control station, is maintained constant by a speed. regulating arrangement. The direct current motor at the control station is mechanically coupled to a high frequency generator ot the inductor type and a low frequency wave is obtained from slip rings connected to opposite commutator bars of the motor. This low frequency wave and the high frequency wave from the synchronous generator are used for synchronizing the operation of the second direct current motor, that is, the one at the controlled station. In order to facilitate the transmission of the low frequency Wave, it is caused to modulate by means of a rela the output of an electro-mechanical osci ator and this modulated wave, together with the high frequexrcy wave generated' by the synchronous genertor,are transmitted overthe same line to the controlled station where after being amplified the are separated b wave filters. The moda ated 'Wave fis passe through a` demodulator, the output current of which operates a polarized relay l causing its contacts to open and close at the frequency enerated at the slip rings of the motor at t e control station. The low frequency square Wave from the contacts of this relay is sup lied to the grid circuit of a three-electro e electric discharge detector 'or supplied from slip) rings connected to oppoars of the motor at the controlled station and the resulting output l current, the value of which is a function of the relative phase of the low frequency 10o the use of waves supplied to the grid and plate cirsuits, is supplied to a regulating field winding of thecontrolled direct current motor. In starting this motor, the action of these low frequency waves through the detector circuit is to pull the two motors into step at the desired phase position and to hold them there within limits of about 20 degrees. After this the high frequency wave from the synchronous generator is supplied through an amplifier to a dynamo electric machine of the inductor type mechanically coupled to the controlled direct current motor. This dynamo electric machine may act as a motor, aiding the direct current motor, or as a generator, opposing the direct current motor, in which case the power generated is dissipated as heat in the machine and amplifier tubes. This high frequency interlock maintains a precise phase position between the two driving motors at some one of a number of points within which they were held by the low frequency interlock. The scanning discs may then 'be adjusted to the relative phase positions required for proper framing of the images by the use of mechanical means which rotates the .stator structurestof the machines at the receiving station. After the two motors are brought into synchronism and the image framed, it has been found that usually the most` satisfactory operation is obtained by using only the high frequency interlock. As is obvious to one skilled in the art, the framing may also be accomplished by the use of suitable mechanical means for rotating the scanning disc on the shaft, or by causing the high frequency machine to slip one pole at a time after disconnecting the low frequency interlock. In order to further increase the accuracy of synchronization, the rotating system at the controlled station is designed to have a momentof inertia small vcompared to that. of control station.

In some cases it may be desirable to transwave for modulating a wave of higher frequency, as explained above. Obviously, if desired, the two synchronizing waves may be transmitted over separate lines. Obviously, for short lines of negligible impedance and substantial power capacity the machines ma be directly connected without devices for synchronizing with the small amounts of power Whichit is possible to transmit over tele hone lines.

The use of both high and low frequency synchronization is desirable for the reason that it is difficult to synchronize on the high frequency alone, since the' motors must be brought to the-samel speed within a cert-aiii limit expressed in rate of change of phase position in electrical degrees. For machines of a large number of poles this will be a very minute difference in speed of rotation. By synchronizin first on the low frequency and then on tIie high frequency much quicker .and more certain synchronization is secured.-

Another advantage of the system lies in the fact that since the low frequency wave has a frequency of one cycle per revolution of the driving motor, the two motors can be synchronized at only one relatively narrow phase position and they are accurately held at a definite point within the limits of that position by the action of the high frcqueny wave. A high frequency interlock alone permits the synchronization of the machine at as many phase positions as there are pairs of poles. This feature of the system is particularly advantageous in system-s which require that the motors be interlocked at one definite phase position, for example, as is required to give accurate framing of the picture in a television sys-` tem as herein' described.

In some systems, particularly where the motor at the controlled station displays a marked tendency to vary in speed, due to power supply voltage fluctuations or tiansmission disturbances such as are to be expected with radio transmission, the continuous use of theV double frequency synclironization may be found advantageous. This is desirable if there is probability of the high frequency control being overcome, in which case the machines would have to be synchronized by the operator if the low frequency interlock were not in use. If, on the contrary, it were in use,vtlie machine would immediately resynchronize, with only a iliomentary disturbance of the transmitted picture.

PM ring to the drawing, there are shown two stations A and B which...comprise a television system of the typedisclo'sed and claimed in the copending application of F. Gray, Serial N 0. 181,538, filed April 6,1927. At the station B, thesubject 101 whose image is to be viewed at the receiving station A bythe receiving operator 102 is located in front of a scanning apparatus. This apparatus comprises an arc lamp 103 and an optical system for causing a slender A .icil of substantially parallel rays of intense light to sweep across the field iii front of the scanning apparatus and scan the subject 101 in a series of successive parallel lines. The optical system includes a scanning disc 10-1 which has a number of small circular a ertures 106 arranged in a spiral exten ing around the disc near its rim. Light from the arc 103 is directed by a lens system 107 soV that anintense beam of light passes through each aperture as it moves across the illuminated area of the disc. An opaque n..aaaliiiliaiaillw `vthe subject is completely scanned once for each revolution of the disc in a series of lsuccessive parallel lines by a small rapidly moving intensely bright spot of light. As the spot of light passes over the subject, light is diffus'ely reflected therefrom and a portion of the reflected light falls on the photo-sensitive surface of a large aperture photo-electric cell 112.4 An electric wave proportional to the intensity of the light is generated. This type of scanning apparatus is described in more detailin the application of Gray referred to above.

The image waves generated in the hoto'- electric cell are amplified in an electrlc discharge amplifier 113 and transmitted through a transformer 114 to a line 115 connecting the transmitting station B with the receiving station A. l

The scanning disc 104 is driven by a direct current motor 20 connected thereto through the shaft 80 and gear box 81. Obviously, thel gear box may be omitted and thedisc 104 mounted directly upon the shaft 80 if desired. The motor 20 is arranged to be driven in synchronism with a control motor 10 located at the receiving station A. The relative location of the control and controlled motors is, in general, immaterial,

the arrangement shown herein being preferable where a' receiving system is arranged to be connected with any one of a number of transmitting stationsf. The operation of the synchronizingcircuit is hereinafter explained in detail.

At the receiving station A the image waves from the line r 115 are transmitted through a transformer 116 to anelectric discharge amplifier 117 in which they are amplified and fed to a neon glow discharge lamp 118 arranged in front of a scanning disc 121 similar in construction to thescanning disc located at the transmitting station B. The disc is driven by the direct current motor 10 connected thereto through. the shaft 90 and the gear box 91. the disc there is located an opaque screen 119 having an opening 120 of such ,size that at one time only one of the apertures of vthe disc 121 is in the field of view of the observer` 102. The lamp'118 is preferably of the type disclosed in detail in the copending application of F. Gray, Serial No. 138,831, filed October 1, 1926. The optical field defined by the opening 120 and illuminated by the light coming from the lamp 118 through the moving apertures of the disc 121 isv viewed In front of by the observer 102without the aid of any optical system. The observer sees at any instant a single aperture in the same relative position as the spot of light on the subject' 101 at the transmitting station BA and the brightness of the aperture corresponds tothe amount of light reflected from, that particular elemental area of the subject. On account of persstency of vision, the observer consequently sees an apparent image ofthe subject on the front surface of the disc 121, complete views of ,the subject being transmitted at the rate of yabout 18 per second so that the subject can be seen in motion.

In order to provide for proper framing-` of the image the direct current motor 10 and the alternatmg current generator 15 are mounted in asuitable cradlmbase160 as By turning the worm 162 in one direction or other by means of thehand wheel 163 the angular position of the statorA structures of the machines 10 and 15 may be`simultaneously changed, thus causing their armatures and consequently the scanning disc to take the phase position required for proper framm0. l

t'lhe circuit for synchronously operating the driving motors 10 and 20-will now be described. Each of these motors is a direct current motor of the compound Wound type having, respectively, series field windings 11 and 21, shunt field windings 12 and 22 and legulating field windings 13 and 423. All of the windings of each motor are cumulative. Each of the motors is provided with a pair of slip rings, 14 and24, respectively,

connected to opposite commutator bars for j,

producing an alternating current of a low I- frequency of one cycle per revolution of the motor. Alternating current generators of the inductor type 15 and 25 are mechanically coupled to the motors 10 and 20, respectively. The generators comprise, respectively, rotors 16 and 26 and stators 17 and 27 on which' are mounted exciting. windings 18v and 28 and generating windings 19 and 29. The generator 25 operates as a synchronous motor, as hereinafter described. j

The speedof the motor 10 is maintained constant by a regulating circuit of the type` described in the'copending application of H. M. Stoller, Serial No. 127,051, filed August 4, 19,26. This regulating circuit comprises a tuned circuit 30 consisting of a condenser 31 and an inductance coil 32 connected in series. This circuit is connected to the generating winding 19 and the terminals of the inductance coil 32 are connected in the anode circuit of a three-electrode electric discharge rectifier or detector 33 for lsupplying space current thereto, the voltage supplied to the anode circuit being proportional to the drop across the inductance coil 32. Connected in series in the anode circuit of the detector 33 is a resistance 34 shunted by condenser 9. This resistance is also connected in the input circuits of the threeelectrode electric discharge devices and 36, so that the grid voltage of these devices is controlled by the potential drop across it. The regulating field winding 13 is connected in the anode circuit of the devices and 36 in series with the source 38. The power suppl for the cathodes of the detector 33. and t 1e devices 35 and 36 and for the anode circuits of the devices 35 and 36 vis obtained from the transformer 37, the primary winding of which is connected to the slip rings 14. The source of power 38 supplies direct current to the motor 10 and also serves as a source of positive grid biasing potential for the devices 35 and 36, the connection being made in series with resistance 34. A condenser 39 is connected in shunt to the regulating field winding 13 to steady the rectified current supplied thereto from the anode circuits of the devices 35 and 36. Two resistances 40 and 41 are connected in series across the regulating field winding 13. The junction of these two resistances is connected to the grid of thedetector 33 through a third resistance 42 and a condenser 43 is connected in shunt to the series circuit comprising resistances 40 and 42.

The motor is started by closing the switches 67 and after it is brought up to speed the switch 44 isclosed, energizing the detector 33 and the devices 35 and 36 so that the normal speed is held constant by the action of the regulating circuit. The tuned circuit 30 is so designed that the frequency of the wave generated in the winding 19 when the motor is running at the desired speed lies on the falling portion of its resonance curve. When the speed of the motor starts to increase, for example, the voltage drop across the inductance 32 decreases, reducing the space current of the detector 33 and consequently the voltage drop across `the resistance 34 which opposes the positive biasing potential limpressed on the grids of the devices 35 and 36 from the source 38,

thus increasing the regulating field current and limiting the rise in the motor speed. The precision of the'circuit Iis increased by the delayed feed-back to the grid of the detector 33. Any increase in the plate current of the devices 35 and 36 increases the voltage drop across the resistance 40 which is applied through the resistance 42 to the grid of the detector 33. However, due to the action of the condenser 43 and the resistance 42, this voltage does not increase iinmediately but lags behind by a time which is proportional to the value of the resistance 42 and the capacity of the condenser 43. This time should n'eferably be of the samel older or greater than the natural period of oscillation of the system. The operation of the circuit to prevent any decrease in the speed of the motor is analogous. The motor 2() is maintained in synchronism with the motor 10 by means of the high frequency wave generated in the winding 19 and the low frequency wave obtained from the slip rings 14. These waves could be transmitted over separate lilies tothe television transmitting station l, but in the circuit herein shown they are arranged to be transmitted over the saine line. As the wave generated at the slip -rings 14 is of low frcquency (of the order of 17 C. P. S.) it is undesirable to transmit it directly over a telephone line. The output of a higher fre- 'e'iuency wave is therefore modulated by this low frequency wave and the resultant modulated wave transmitted to the station B.

This higher frequency wave, which was, as used, of the order of 760 cycles per second, for example, is generated by an oscillator 130 which is preferably of the electromechanical type, as described in the copending application of C. R. Moore, Serial No. 48,223, filed August 5, 1925. The output of the oscillator is connected through the transformer 131, the secondary winding of which is shunted by a high resistance 132. to thel input of the low pass filter 133. The terminals of the secondary windings of the, transformer 131 are connected to the contact and armature of the relay 134, the winding of which is connected through the leads 46 to the slip rings 14 so that the output ot' the oscillator is short circuited at the fre quency of the wave generated at the slip 1m rings 14, thus modulating the 760 cycle wave from the oscillator. This modulated wave is transmitted through the low pass filter 133 and the transformer 135 to the line 136 A which connects the stations A and B. The generator winding 19 is connected through the leads 45 to the input terminals of the high pass filter 137 the output terminals of which are connected Ito the transformer 135 so that the high frequency wave is also transmitted over the line 136 to the station B.

At the station B the high frequency wave and the modulated wave are transmitted through the transformer 138 to the electric discharge amplifier 139. Connected in parallel to the output of the amplifier 139 are the high pass lter'140 and the low pass filter 141. The high pass filter 140 is designed to select the high frequency wave` generated in the winding 19, and the low lia) space current batteries.

pass filter 141 is designed to select the modu-l lated wave which is then transmitted` through the transformer 142 to the electric discharge demodulator 143.

This demodulator is provided with the usual cathode heating, y grid biasing and Connected to the output of the demodulator 143 are the windings of a polarized relay 144, the amature of which is operated by the demodulated current at the frequency of the wave generated at the slip rings 14. The operation of the relay produces a square-top wave of interrupted current from the batteryl 145. This wave and the high frequency wave in the output of the filter 140 are employed for operating, the motor 20 in synchronism with the motor 10.

The synchronizing circuit comprises a push-pull control or detector circuit D employing two three-electrode discharge devices v47 and 48, and a push-pull amplifier Am employing two three-electrode discharge devices 49 and3 50. The cathodes of the four devices are supplied with heating current from the 110 volt line 51-52. This line also supplies grid biasin potential to the devices 49 and 50 through t ye resistances 54 and 55. Space current for the devices 49 and 50 is supplied from v the 750 volt line til-53. Space current is supplied to the devices 47 and 48 yfrom the 110 volt line 51-52 and the transformer 58, the primary Winding of which is connected to the slip rings 24. The low frequency wave from the relay 144 is supplied to the input circuit ofthe detectors 47 and 48. The regulator field winding 23 is connected in the output circuit of the detector vD to receive rectified current therefrom, and condenser 59 is provided for bypassing the alternating component of this current. Condenser 60 is for the purpose of power factor correction, neutralizing the lagging current drawn by transformer 58 which is .built to draw an unusually heavy magnetizing current. This transformer condenser combination acts to'prevent hunting of the regulated motor system. The value of the current supplied to theregulating field 23 depends upon the relative phase ofk the lowv frequency waves supplied\ to the input and output circuits of t e de- `tector D so that this portion of the synchronizing circuit operates to maintain the speed of the motor 2O such'that the wave from the slip rings 24 is in an ap roximately constant phase relation with t e corresponding low frequenry wave from the rela 144 in a manner similar to the operation o the regulating circuit described in Patent No. 1,663,- 890 to H. M. Stoller, March 27, 1928. The high pass filter 140 is connected to the amlier Am throu h the leads 150 and transrmer 151 so t at the high frequency is lagain amplified and supphed through the output transformer 61 to the winding 28, driving the machine 25 as a synchronous motor, thus holding the motor 20 substantially exactly in phase with the motor 10. A condenser 62 is connected in series with the secondary winding of .the transformer 61 and the winding 28 to'tune the circuit to a frequency a little higher than the synchronous frequency of the machine 25. This tends to prevent hunting as described in the application of E. R. Morton, Serial N o. 181,324, filed April 6, 1927.

The operation of the synchronizing circuit is, as follows: The switches 63 are closed to bring the motor up to speed. Then the switch 64 is closed, putting the detector circuit D into operation to bring the motor 2() approximately into step with the motor 10 after which the switch 65 is closed and themachine held in exact synchronism through the action of the high frequency waves. After the machines are thus brought into synchronism the phase position of the scanning disc 121 .can be adjusted to the position required for proper framing of the image byl turning the hand wh el 163. The lo7 frequency interlock may t en be disconnected and the high frequency interlock employed alone for maintainlng synchronous operation.

However, as explained above, -it may be desirable in some cases to continuously employ both interlocks in order to maintain most satisfactory operation. Y

In one system in? Which the frequencies o the low and high frequency waves were respectively 17.7 and 2125 cycles per second, it was found possible to maintain phase positions of the motor Within 0.05 under ordinary variations of voltage and load.

For best operationit is desirable that the ing station A at which the large scanning disc 121 is used and locating the controlled motor 20at the transmitting station where the smaller scanning disc 104 is used.

What is claimed is:

1. In combination, means including scanning apparatus for producing image forming waves, means including a second scanning apparatus for producing an image corresponding to said waves, .mechanically independent means for drivmg each of said scanning a paratus, means for obtaining a wave of a gequency of one cycle per second per revolution of one'of rsaid drivmg means,

means controlled by said last mentioned wave for pulling said other driving means approximately into a desired phase relation with respect to said first driving ,-,ineans, means for obtaining a wave of high frequency proportional to the speed of said first driving means, and a synchronous motor mechanically coupled to said other driving means and arranged to be driven by said high frequency Wave to maintain said driving means at one of a plurality of phase positions, within a range of position determined by said low frequency wave, with respect to said first driving means.

2. In combination, means including a rotatable scanning disefor producing image forming waves, means including a second rotatable scanning disc for producing an image corresponding to said waves, nicchanical independent means for driving cach of said scanning discs, means for obtaining a Wave of high frequency proportional to' the speed of one of said driving means, a synchronous motor mechanically coupled to said other driving means and arranged to be Y driven by said high frequency wave vto main-- tain said driving means in substantially exact synehroiiisin with said first driving means, and means for pulling said second driving means approximately into a desired phase relation with respect to said first driving means.

3. A combination according to the preceding claim in which the moment of inertia of the rotating apparatus associated with said second driving means. is small coni-` pared to the moment of inertia of the rotating apparatus associated with said first driving means. l

4. In combination, means including a rotatable scanning disc for producing image forming Waves, means including a second rotatable scanning disc for producing an image corresponding to said Waves, afmotor for driving each of said scanning discs, a source of waves of frequency of one cycle per second per revolution of one of said scannin discs, a source of carrier Waves, means or modulating said carrier waves in accordance with Waves from said first mentioned source, means for demodulating'said modulated carrier waves, a'line interconnecting said modulating and demodulatiiig means, means controlled by said demodulated wave for pulling said' other motor approximately into a desired phase relation with respect to said first motor, a source of Waves of high frequency proportional to the speed of said first motor, a synchronous motor mechanically coupled to said other motor, and means including at least a portion of the line interconnecting said vmodulating and demodulating means for impressing said high frequency wave on said synchro-- nous motor to maintain said second motorin substantially exact synchronism with said first motor.

5. Means for framing an image in a television receiving system comprising a low frequency interlock between the transmitting t and receiving moving scanning elements for maintaining the relative positions of said elements fixed within narrow limits, means for accurately holding the relative positions of said elements at an one of a plurality of points within said 'mits, and manually controlled means for permitting a proper choice of said plurality of points.

6. Television ap aratus comprising a scanningr element for t e receiving station, means including a motor for continuously operating said scanning element in synchronisni with a scanning mechanism at the transmitting station, and means for framing. the image at the receivin station comprising means for slowly varying the speed of said motor while it is running. 4

7. Television apparatus comprising a scanning elemeiit for the receiving station, a motor for continuously operating 4said scannin element in synchronism with scanning mec anism at the transmitting station, and means for framing the image at the receiving station comprising means for varying the instantaneous speed of said motor to obtain a quick but rough adjustment and additional means for obtaining a more accurate adjustment.

8. In an electro-o tical image producing-- system, means inclu ing a rotatable element and driving means therefor for scanning the elemental areas of an object in succession, thereby producing an image current, means including a source of light responsive to said image current for producing the light tones of elemental areas of the image, means including a second rotatable element andv driving means therefor for controlling the position of the light tones of the elemental areas of the image, means for obtaining aV wave of relatively low fr uency propor tional to the' speed oone o saidrotatable elements, means res nsive to said wave for placing the other o said rotatable elements in approximate synchronism with said one rotatable element, means for obtaining a wave of comparatively high frequency proportional to the speed of said first rotatable element, and means responsive to said high frequency wave for further controllingft-he movement of said second rotatable element, whereby the low frequency wave and the high frequency Wave are utilized jointly for obtaining the 'correct positionin of the elemental areas of the ima-ge wit respect to Athe corresponding elemental areas of the object.

9. The method of producing images electro-optically which comprises scanninuan ch object to produce an image current w varies in accordance with the tone velues of .successively scanned elemental areas of said object, controllingthe intensity of` a light beam in accordance with the variations of said imufre current, moving said light beam for prodnucing the light tones of the elemental areas ofthe image in succession, producing a wave of relatively 10W frequency proportional to the speed of said scanning, producing u second wave of relatively high frequency proportional to the speed of said scanning, and utilizing said low frequency wave and said high frequency Wave jointly for obtaining the correct movement of said light beam with respect to the scanning of the object.

In witness whereof, we hereunto subscribe cur names this 17th day of June A. D., 1927.

HUGH M. STOLLER. EDMUND R. MORTON. 

